Add hints for instance variables in console.EmailBackend (#1200)

django-stubs/core/mail/backends/console.pyi

@@ -1,3 +1,8 @@
+import threading
+from typing import TextIO
+
 from django.core.mail.backends.base import BaseEmailBackend
 
-class EmailBackend(BaseEmailBackend): ...
+class EmailBackend(BaseEmailBackend):
+    stream: TextIO = ...
+    _lock: threading.RLock = ...